TRAMP addresses the scientific and technical details of the origin and potential use of the giant piezoresponse observed in silicon nano-objects. After a 10 year debate about the veracity of the giant piezoresistance (PZR) in silicon nanowires, the TRAMP partners (all of whom have been visible participants in this debate) have preliminary evidence for a giant piezocapacitive (PZC) effect. Experiments suggest a central role for stress-induced changes to the charge state of intrinsic defects at the silicon/oxide interface (specifically the Pb0 defect). The capacitive (rather than resistive) nature of the phenomenon is a surprise and the TRAMP partners have the opportunity to be ‘first-in-field’, both in terms of the fundamental science, but also for device applications of this novel phenomenon that occurs in scalable, top-down fabricated silicon nano-objects. In the initial phase of the project, the TRAMP partners will fabricate ohmically contacted, top-down silicon nanomembranes to be tested in a taylor-made apparatus that allows for the frequency and voltage dependence of the piezoresponse to be measured under uniaxial tensile and compressive stresses up to ˜150 MPa. The dependence of the piezoresponse on doping, temperature and nano-object geometry will be explored and then used to improve the design of a second process batch. This method of rapid prototyping has been used previously by the TRAMP partners, and will yield a map of the relative importance of the PZR and PZC responses as a function of these parameters. This is not only essential from the point of view of developing a microscopic understanding of the phenomenon, but also in terms of optimizing conditions for its use as a stress or motion transduction mechanism. Proper characterization of the piezoresponse will employ two techniques specifically adapted to nano-objects: micro-Raman spectroscopy for the measurement of the local stress in nano-objects, with the option to use TERS for the smallest objects, and Laplace current transient spectroscopy for the identification of the electromechanically active defects thought to be responsible for the giant, anomalous piezoresponse. This latter method is not yet widely used but is adapted to defect spectroscopy on any electrically connected nano-objects whose capacitance is too small to permit the use of more traditional capacitive spectroscopies. Once the optimal conditions (i.e. for maximum, stable PZC) have been determined, the TRAMP partners will undertake a technical study of two potential applications: the electrical detection of process induced microstrains in the active layer of ultra-thin commercial silicon-on-insulator wafers for quality control purposes; and as a means to detect motion in a nano-mechanical resonator where standard optical or capacitive methods lose sensitivity. The second application requires the fabrication of in-plane nanoresonators in which the TRAMP partners are expert. In the final task of the project the results of these two technical studies will be used as the basis for discussions with potential industrial partners. Impacts of a successful TRAMP project will therefore include high visible scientific and technical results, the first steps in the characterization of devices exploiting the PZC that are based on a scalable, top-down silicon technology, the patenting of intellectual property, and exploratory talks with partners from the semiconductor manufacturing industry aimed at licensing or collaborative opportunities.

Perovskite solar cells (PSCs) have become a trending technology in photovoltaic research due to a rapid increase in efficiency in recent years. In 2020, a record efficiency of 25.5% close from Shockley-Queisser theoretical limit of 30% was reported. Tandem solar cells offer an alternative to go beyond but stability still remains an issue. In our project, we will bring together our complementary expertise in molecular and macromolecular syntheses, thin film morphology tuning and cell device engineering to improve the stability of highly efficient inverted perovskite cells using new electron transport layers (ETL) with high electron mobility and high stability. We will design and synthesize new n-type fullerene free semiconductors. Introduction of cross-linkable groups will lead to stabilized ETLs by thermally-induced cross-linking after film formation. The efficiency and stability of these ETLs will be finally evaluated through their incorporation in tandem configuration.

Thin-film (TF) silicon solar cells deposited by plasma enhanced chemical vapor deposition (PECVD) remain the most economically viable photovoltaic (PV) technology because they combine abundant low-cost material and low-cost, large area, low-temperature processes. The best candidate to achieve the lowest intrinsic manufacturing cost-per-Watt (€/W) is the "micromorph" device, which is a tandem cell combining a hydrogenated amorphous silicon (a-Si:H) wide-gap top-cell, and a hydrogenated microcrystalline silicon (µc-Si:H) low-gap bottom cell. Such a tandem cell usefully absorbs a large part of the solar spectrum while reducing thermalisation losses compared to single junction cells. However, this technology suffers from the still low absolute-value of its PV efficiency (best cells around 12%, modules around 10%) compared to more expensive technologies such as crystalline silicon (premium modules above 20%). The APOCALYPSO project aims to address this issue and achieve significantly greater stabilized efficiencies for micromorph devices deposited and processed at low-temperatures with an objective above 14%. It targets a discontinuous improvement in three device parameters: (1) end-of-life collection efficiency of the a-Si:H cell, (2) output voltage of the µc-Si:H cell, and (3) photon management and absorption. It will achieve these goals through the use of two novel concepts: the plasma processing of layers using non-sinusoidal "Tailored" Voltage Waveforms (TVWs), and the incorporation of Selectively Transparent and Conducting Photonic Crystals (STCPCs), deposited using large-area techniques. The first concept, the use of TVW's to excite a capacitively coupled processing plasma, involves applying a voltage waveform that resembles a sequence of either "peaks" or "valleys" to the powered electrode, splitting the sheath voltage at the edge of the plasma unequally between itself and the substrate holder, while keeping the plasma density constant. One can thus separate these two critical process parameters, and gain new control over material quality. The TVW technique will be applied to multiple processes for a micromorph cell: the post-deposition treatment of the doped ZnO to reduce shunting, the deposition of the a-Si:H top cell layer to improve cell stability, and the deposition of the µc-Si:H layer to augment layer quality. Application of this technology at these three process points offers significant leverage over material quality and thus device efficiency with no additional manufacturing cost. The second concept, the use of STCPCs involves the integrated use of alternating layers of subwavelength silica nanoparticle and sputtered indium tin oxide (ITO) conducting films. The resulting one-dimensional photonic crystals exhibit broad and intense Bragg-reflection peaks and are highly transmissive over the spectral regions outside their stop-gaps . These stacks have conductivities comparable to ITO due to infiltration and coating of the nanoparticles by the sputtered ITO, creating a continuous electrical network. This unique combination of optical and electrical properties of silica nanoparticle-based STCPCs render them highly effective tuneable solar spectrum splitters. These STCPCs will be integrated as conducting intermediate photonic crystals in micromorph cells to optimally couple spectrally relevant light in the top and bottom cells and thus enhance a balanced distribution of the photogenerated current. Through the implementation of these new concepts, the project objective is to increase the conversion efficiency of thin-film silicon PV beyond 14% using only techniques that are low-cost and scalable to large areas. The success of the project relies on the complementary expertise in the two novel TVW and STCPC concepts that is solely available from French and Canadian partners, respectively, and thus requires the international Franco-Canadian collaboration along with the task distribution described in this proposal.

The SMASH-IBC2 project aims at reducing the cost of PV electricity by developing innovative high efficiency solar cells and modules. Two different technologies currently dominate the PV market. The first one is based on crystalline silicon (c-Si) devices which historically lead the market due to its proven reliability and efficiency. Thin film technologies also show a great potential in terms of efficiency and cost reduction. In this project both technologies will be merged to obtain high efficiency solar cells on thin c-Si wafers with simplified processes. This may be achieved through an innovative solar cell design called IBC Si-HJ (Interdigitated Back Contact Silicon Hetero-Junction). IBC Si-HJ cells have a high efficiency potential (=25%) achievable on thin wafers (=100µm) with a low temperature fabrication process (=200°C). Moreover a simplified and aesthetic module interconnection (coplanar) can be developed with these structures. To obtain a cost effective structure we will study different processes from the thin film technology and try to transfer them for c-Si solar cells fabrication. We will focus on one hand on thin layers and contact formation (chemical and physical vapor deposition, electrodeposition, epitaxy). On the other hand, simplified cell fabrication steps (laser contacting, ablation and scribing) will be developed to achieve a low cost and industrial process. The main goal of the project is to validate a cost-effective method for fabricating high efficiency PV modules, using 24% efficient c-Si solar cells, based on thin (100 µm) and large area (150 cm2) silicon wafers. The metallisation of these devices will be ITO- (Indium Tin Oxide) and Ag-free to reduce the cell cost. This achievement will be based on well identified scientifical and technological issues linked with different tasks in the project. Thanks to the previous projects on the same topic (QC-Passi, SHARCC, TopShot), an important knowledge has been developed by the different partners. A precise and realistic roadmap has therefore been determined, as well as associated milestones.

Industry is currently taking the lead to develop applications based on the genuine properties of Single Walled Carbon Nanotubes (SWNTs), that are their outstanding strength and aspect ratio, and ability to display metallic or semi-conducting characteristics, depending on their chiral structure. From a fundamental point of view, and also to make these applications commercially viable, finding a way to grow, on demand, metallic (m-) or semi-conducting (sc-) SWNTs with a reasonable yield and good selectivity, remains the biggest issue. The Catalytic Chemical Vapor Deposition (CVD) synthesis of SWNTs, that takes place at high temperature (600-1200 C), and in a complex chemical environment, is still not completely understood, though recent experiments, reporting a chiral selective growth, ignited a burst of questions, and new efforts to tackle this issue. In this context, the goal of the GIANT project is to build upon recent breakthrough results obtained in the understanding of the growth mechanisms, to gain an effective control of SWNT structure during their synthesis. In a previous project, involving the same partners, the importance of controlling the growth mode characterizing the geometry of the tube / catalyst nanoparticle (NP) interface during the growth, has been emphasized. A thermodynamic modeling relating interfacial energies to the resulting tube chirality has been developed. We also showed that using bi-metallic NPs, and fine tuning the growth conditions, led to a better SC/M selectivity. The underlying idea is now to focus on the chemistry and structure of the tube / NP interfaces using dedicated new experiments. Guided by the understanding brought about by our modeling, we will develop new catalysts, by different methods, including our original route based on the grafting and calcination of Prussian Blue Analogs, that enables to form dispersed, stable bimetallic and carbide NPs with controlled stoichiometry. Real time, in situ investigations will shed new light on observations that were previously done after growth. A strong asset of this project will be the use of the NanoMAX HR-TEM facility, that combines state of the art environmental Transmission Electron Microscopy (TEM), with original developments of the gas injection system, that make it perform under the same conditions as the UHV-CVD setup used in the laboratory. The chemical and structural evolution of the catalysts will be also investigated in situ and real time in a dedicated facility (FENIX) at LPICM. Systematic cross-checking between TEM (imaging and diffraction) and Raman assignments of the chiral distributions of produced tubes, and a comparison of in situ data with advanced post growth characterizations will be performed. Theory and modeling will be in constant interaction with experiments, either to guide the choice and modifications of the catalysts or to help the interpretation of the results. The thermodynamic modeling of the interface will be extended to include growth kinetics, and detailed atomistic Monte Carlo computer simulations of two kind of systems with different affinities for C (from NiPt to W or Mo carbide NPs) will be performed, to check their influence on the growth modes and resulting chiralities. Each catalytic system family (NiPt, CoMo and CoW, WC or Mo2C, carbon precursors and growth conditions) will be iteratively analyzed, tested for its selective growth ability, and, if successful, eventually used for producing m- or sc-SWNTs incorporated in different types of devices (sensors, transistors, field emission tips …). A successful outcome of the project will be the identification of selective catalytic systems offering either sc- or m-selectivity, with a reasonable yield, and the understanding of the underlying mechanisms.